He was also alarmed that she was being regularly photographed laden with designer bags in the same way as Wayne Rooney's fiancee Coleen McLoughlin.

As a result, 25-year-old Miss Middleton has been working for the High Street clothing firm Jigsaw at their headquarters in Kew, West London, for the past seven weeks as an assistant buyer for the firm's junior accessories line.

She secured the job through her mother, Carole, who helps design the Jigsaw Junior website and is friendly with the company owners John and Belle Robinson, at whose Mustique villa Kate and William holidayed earlier this year.

Unlike other assistant buyers at the firm, however, she works only four days a week - Monday to Thursday - allowing her to arrange her schedule round that of William, who is due to start duties with the Household Cavalry's Blues and Royals Regiment.

And despite being so new to the payroll, she was still given permission to take almost three weeks' holiday over Christmas and the New Year.

'Kate has tried her hand at a number of projects since leaving St Andrews, most notably setting up her own childrenswear firm,' a friend of the prince explained.

'But for one reason or another, not least her relationship with William, they have fallen by the wayside.

'Although William understands how difficult dating a royal can be and is very supportive of his girlfriend, he became quite sensitive about the way she was perceived.

He was particularly concerned that it looked like she was on one long shopping trip, whiling away her time while waiting for him to propose.

'The job at Jigsaw was the perfect solution as Kate is interested in fashion and, because of her parents' business, has a great gut instinct for what appeals to children.'

Kate's job involves meeting suppliers and deciding which stock - such as socks, tights and hair slides - to buy in for the firm. While her working hours have raised eyebrows she does, however, get on well with her new colleagues.

Shortly before Christmas a couple of workmates even played a practical joke by doctoring a £20 note, swapping the Queen's face for a photograph of Kate with the words HRH Katy underneath.

Kate is said to have roared with laughter when she spotted the note, which had been left on her desk, and even took a copy home to show William.

In recent weeks she has also confided in friends about the seriousness of her relationship with William which is likely to spark further speculation that an engagement is on the cards.

'She hates it when people try to make out that her relationship with Willy is just another university romance,' said a source. 'As far as she is concerned, it is definitely the real thing.'